Demand for high-speed communication is increasing in fields such as of automobiles. Transmission characteristics of a cable used for high-speed communication such as a characteristic impedance thereof have to be controlled strictly. For example, a characteristic impedance of a cable used for Ethernet communication has to be controlled to be 100±10Ω.
A characteristic impedance of a communication cable depends on specific features thereof such as a diameter of a conductor and type and thickness of an insulation coating. For example, Patent Document 1 (JP2005-32583A) discloses a shielded communication cable containing a twisted pair that contains a pair of insulated cores twisted with each other, each insulated core containing a conductor and an insulator covering the conductor. The cable further contains a metal-foil shield covering the twisted pair, a grounding wire electrically continuous with the shield, and a sheath that covers the twisted pair, the grounding wire, and the shield together. The cable has a characteristic impedance of 100±10Ω. The insulated cores used in Patent Document 1 have a conductor diameter of 0.55 mm, and the insulator covering the conductor has a thickness of 0.35 to 0.45 mm.